This invention relates to the field of reactor purification systems. More particularly, this invention relates to reducing residual oxygen levels within the processing chamber of an atmospheric reactor.
Atmospheric reactors are used in a number of different semiconductor manufacturing processes. For example, atmospheric annealers, rapid thermal processing systems, and chemical vapor deposition systems are all used at different points in wafer processing. The designation of xe2x80x9catmosphericxe2x80x9d indicates that the processes performed within the processing chamber of the atmospheric reactor tend to be done at a pressure that is relatively near atmospheric pressure, rather than at a pressure that is significantly reduced below or pressurized above atmospheric pressure.
For example, an atmospheric process performed within the processing chamber of an atmospheric reactor might be performed using a process gas at an overpressure of about thirty Torr or so. One benefit of atmospheric reactors is that they do not need to be designed to withstand either very high or very low pressures, which allows for a relatively simplified design and resultant relatively lower cost for the system.
Although the processes within the atmospheric reactor are conducted at pressures that are near that of the ambient atmosphere, this is not to say that the atmospheric reactor is preferably exposed to the ambient atmospheric environment. Atmospheric reactors are typically isolated from the ambient atmospheric environment, such as by load locks, so that the conditions within the atmospheric reactor can be rigorously maintained according to predetermined standards of residual gas content, moisture content, cleanliness, etc.
Different process gases are used within the processing chamber of the atmospheric reactor depending upon the specific process that is performed within the processing chamber. Some of the process gases used for one process conducted within the processing chamber may be incompatible with a different process that is to be performed at a later point in time within the same processing chamber.
For example, oxygen is used as a process gas during a silicon oxidation process in an atmospheric rapid thermal processing system. Silicon oxidation processes are typically performed at regular intervals as a means to determine the uniformity of the heat processing provided by the rapid thermal processing system. This is done by measuring the thickness of the silicon oxide formed across the surface of the silicon wafer during the silicon oxidation process. However, regardless of the specific process or situation by which oxygen is introduced into the processing chamber, some amount of oxygen typically remains within the processing chamber of the rapid thermal processing system after the process is concluded. The residual oxygen left in the processing chamber tends to create problems with other processes that are to be performed within the processing chamber.
Therefore, after the processing chamber of the atmospheric reactor is exposed to oxygen, it is desirable to purge the residual oxygen from the processing chamber of the atmospheric reactor to a level below that at which it adversely effects subsequent processes. This is typically accomplished by blowing a relatively inert gas, such as nitrogen, through the processing chamber of the atmospheric reactor. However, purging an inert gas through the processing chamber tends to be a relatively inefficient method of reducing the level of the residual oxygen remaining within the processing chamber, and tends to require as long as an hour or more to decrease the residual oxygen level to a tolerable level. The length of time required for the nitrogen purge tends to reduce wafer throughput and thereby increases manufacturing costs.
Thus, there is a need for a system for reducing residual oxygen levels within the processing chamber of an atmospheric reactor.
The needs expressed above, and other needs, are met by an apparatus for reducing residual oxygen content from a processing chamber of an atmospheric reactor after the processing chamber of the atmospheric reactor has been exposed to an oxygen environment. The processing chamber of the atmospheric reactor has an inert gas purge, including an inert gas source, for reducing a residual oxygen level within the processing chamber of the atmospheric reactor at a rate of reduction. A venturi vacuum system is enabled by the inert gas source. The venturi vacuum system draws a vacuum on the processing chamber of the atmospheric reactor and supplements the inert gas purge, thereby accelerating the rate at which the residual oxygen level is reduced within the processing chamber of the atmospheric reactor.
In this manner, the vacuum created by the venturi vacuum system increases the efficiency of the inert gas purge by reducing by some moderate degree the pressure within the processing chamber of the atmospheric reactor. This provides additional gas flow within the processing chamber to physically remove the residual oxygen from the processing chamber. However, the vacuum provided by the venturi vacuum system is not high enough to cause damage to the components of the atmospheric reactor, which are not designed to withstand the forces that are created by a relatively high vacuum. In preferred embodiments, the venturi vacuum system and the inert gas purge are configured to operate alternately in a cyclical fashion.
In an alternate embodiment of the atmospheric reactor, a wafer transfer mechanism is used to move wafers into and out of the processing chamber. The wafer transfer mechanism includes a metallic gettering agent, which reduces the residual oxygen level in the processing chamber of the atmospheric reactor. In a preferred embodiment, the metallic gettering agent is titanium. In this manner, residual oxygen within the processing chamber is reacted with the titanium elements of the wafer transfer mechanism, and thus the level of residual oxygen within the processing chamber is reduced.
A further embodiment of the invention includes a method for reducing the residual oxygen content from a processing chamber of an atmospheric reactor after the processing chamber of the atmospheric reactor has been exposed to an oxygen environment. Non-production wafers are prepared, which include a metallic gettering agent. The metallic gettering agent is for gettering residual oxygen from the processing chamber of the atmospheric reactor. One of the metallic gettering non-production wafers is introduced into the processing chamber of the atmospheric reactor. The residual oxygen in the processing chamber of the atmospheric reactor is gettered with the metallic gettering non-production wafers. The preparation and introduction of the metallic gettering non-production wafers is repeated as the metallic gettering non-production wafers become saturated with residual oxygen.
In a preferred embodiment the metallic gettering agent is titanium, which is sputtered onto the non-production wafers. Alternately, the non-production wafers are formed of solid disks of titanium. Gettering of the residual oxygen within the processing chamber is preferably enhanced by elevating the system to a temperature of between about 480 centigrade and about 1,000 centigrade.